Prior to the present invention, E-64 has been the only known epoxysuccinic acid compound possessing thiol protease inhibitory activity together with anti-inflammatory activity as described in U.S. Pat. No. 3,911,111. This compound, however, has an undesirable side effect, i.e., the acceleration of vascular permeability.
The novel epoxysuccinic acid derivatives of the present invention are distinguished from the prior art patented compound by their excellent thiol protease inhibitory activity and anti-inflammatory activity and by the absence of the acceleration of vascular permeability as shown in tests upon laboratory animals.